The invention relates to a display unit, such as a house number display, a traffic sign, or an advertising display unit, consisting of a light guide panel with at least one electrical illuminating element arranged in the vicinity of at least one lateral edge limit and with symbols to be illuminated by the light guide panel.
In the case of such a display unit as described in the German specification No. 3,825,436 LED's were proposed as illuminating elements which were placed in marginal holes with a suitable diameter in the light guide panel. In such a unit the light of the illuminating elements directed into the light guide panel is generally only able to leave the light guide panel at contact points or cut edges, since in other parts there is an essentially total reflection at the lateral faces. For this reason all lateral limiting edges are provided with a reflecting coating, which reflects the light at this position back into the panel. Thus, exit of the light is only able to take place at the position at which the display symbols are mounted. It is in this manner that it is possible to ensure a high light yield or efficient use of the light so that large panels as well may be used without requiring very much energy, energy such as electrical energy, or they may even be operated with solar energy.
The disadvantage of this known design is that the LED's generally have a diameter of 5 mm, and there are also other LED's with a diameter of 8 and 10 mm. More particularly in the case of light guide panels with very large dimensions there is a desire to use LED's with larger diameters for more light. In this known display unit it is therefore necessary for the thickness of the light guide panel to be made suitably large so that light guide panels with a thickness of 8 to 14 mm are necessary, which are provided with holes of a suitable diameter so that large LED's may be mounted therein. Since however it is specifically large light guide panels which call for LED's with large diameters, such light guide panels are very heavy and expensive. A further factor is that mass produced fluorescent light guide panels are generally only obtainable with a thickness of 3 mm so that expensive customized products are required which are subject to minimum orders.